Complex Regional Pain Syndrome (CRPS) refers to a chronic neuropathic pain condition with a broad and varied range of clinical presentations. CRPS patients experience severe pain out of proportion to their original injury, and this may start at the time of injury or weeks later. The pain is described as deep-seated and burning/aching/shooting. Sesnory changes are common, including hypo/hyperesthesia, hypo/hyperalgesia, and allodynia. For instance, many patients describe not being able to tolerate the sensation of bedsheets on their painful limb.

In the affected area, there is often marked edema, temperature asymmetry (usually cooler), and sweating changes (usually increased). Loss of hair and nail growth is common, and disuse of the limb can result in weakness, muscle atrophy, and contractures.

The diagnosis is made clinically, using the Budapest Criteria. Some pain physicians use a nuclear medicine test, three-phase bone scintigraphy, for CRPS diagnosis but this test is becoming less popular, since it has a low positive predictive value.

CRPS is classified as Type I when there is no apparent history of nerve damage, and Type II when associated with definite peripheral nerve injury. CRPS most commonly occurs following fractures and immobilization, but can happen even with little to no trauma.The pathophysiology is thought to involve autonomic dysfunction and inflammation, but much is still unknown.

CRPS affects females about 2-4 times more often than males, and onset is usually in middle age (though there are rare pediatric cases reported). It is a progressive disease that can result in spread of pain, sensory disturbances, and physical changes to other limbs.